Clinical assessment of the relationship between the third molar and the inferior alveolar canal using panoramic images and computed tomography.
OBJECTIVE
To predict the relationship between lower third molars and the inferior alveolar canal (IAC) from panoramic radiographs, and to establish criteria for using computed tomography (CT).


METHODS
A retrospective cohort study was performed involving 443 patients (695 teeth). Predictor variables were the distance between the third molar and the IAC, and findings according to the Rood's criteria. Outcome variables were the absence of cortication between the third molar and the IAC on the CT image, and injury of the inferior alveolar nerve (IAN). Statistical analysis was performed to assess the relationship between predictor and outcome variables.


RESULTS
All patients had preoperative panoramic radiographs, and 71 patients (119 teeth) also had CT images. On CT examination, 48 teeth (40.3%) showed absence of cortication. Injury of the IAN was reported in 7 cases (1.0%), 5 of which exhibited absence of cortication; the remaining 2 did not have CT scans. Five of the 48 cases showing absence of cortication exhibited IAN injury, and none of the cases with cortication exhibited IAN injury. On the panoramic images, the following signs were strongly correlated with absence of cortication: a superimposed relationship between the third molar and the IAC; darkness of the root; and diversion and narrowing of the IAC.


CONCLUSIONS
Presence of Rood's criteria was a predictor for a contact relationship between the third molar and the IAC, and an indication for CT examination. However, a superimposed relationship and the absence of Rood's criteria did not necessarily signify a separate relationship between third molar and the IAC.
Nakamori
Kenji
K
Department of Oral Surgery, Sapporo Medical University, Sapporo, Japan. nakamori@sapmed.ac.jp
Fujiwara
Kumiko
K
Miyazaki
Akihiro
A
Tomihara
Kei
K
Tsuji
Manabu
M
Nakai
Mitsuyoshi
M
Michifuri
Yoshitaka
Y
Suzuki
Rina
R
Komai
Kiyoto
K
Shimanishi
Makoto
M
Hiratsuka
Hiroyoshi
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D016009:Chi-Square Distribution; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008046:Lip / Q000503:physiopathology; D016015:Logistic Models; D008297:Male; D008340:Mandibular Nerve / Q000000981:diagnostic imaging*; D008875:Middle Aged; D008964:Molar, Third / Q000000981:diagnostic imaging* / Q000601:surgery*; D010292:Paresthesia / Q000209:etiology; D011237:Predictive Value of Tests; D011862:Radiography, Panoramic; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D014081:Tooth Extraction / Q000009:adverse effects*; D061221:Trigeminal Nerve Injuries